Krystyna Pienkowski is chairwoman of "An Evening in Krakow," the annual Polonaise Ball to be sponsored by Polish Arts Club of Buffalo Oct. 20 in the Statler Towers Rendezvous Room. Irene Pawlowski is co-chairwoman. Cocktails at 6:30 p.m. will precede dinner. Music will be by the Stefan Mierzwa Continental Orchestra of St. Catharines, Ont., and dancing will begin with the traditional polonaise. Dancers from Arthur Murray Dance Studio of Amherst will entertain with the fox-trot, rhumba, swing and tango. Pienkowski is taking reservations at 839-4480 through Oct. 11. Proceeds benefit the club's scholarship fund.